Copyright 2013 Scripps Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

TULSA - It's a face no one has seen in more than 20 years, but all these years later her family still can't hold back the tears.

"It's like it's getting harder and harder really," said Catherine Riles, the mother of Greta Riles.

In the hot Tulsa summer of 1991, 22-year-old Greta vanished without a trace.

"It would mean everything to know something," said Catherine. "It would mean the world to me."

"I love her and I miss her and I wish she was home," said Greta's sister, Tammy Johnson.

Greta's family did not report her missing.

They say she lived a troubled life. And shortly before her disappearance had a fight with her grandmother.

They figured she had run away.

"Usually if I don't see her over a certain length of time she comes back home," said her mother. "If I'm in Tulsa or Oklahoma City, she finds us."

But this time she never did. And finally in 2012, the family reported her missing to Tulsa police.

When detectives at TPD started looking into the case they found some surprising information. Greta had trouble with the law. After being convicted of a drug charge, she stopped all contact with her probation officer in 1991.

And no one has heard from her since.

"People stray from their family and stray from what they know when they're under the influence of a substance," said Jill Roberson with the Tulsa Police Department's Crime Stoppers unit.

Greta's mother is all too familiar with this kind of pain. In an un-related incident, one of her other daughters was murdered.

"It's like my whole life changed," said her mother crying.

The family says Greta promised that when she got her life together she would come back and take care of them.

Twenty-two years later, they're still waiting.

Greta Riles' last known address was near 61st and Union in west Tulsa. She's 5 feet-two inches tall.

If you know where Greta could be crime call Crime Stoppers at 918-596-cops. You can remain anonymous. Crime Stoppers does not want your name, just your information!

Tips could result in a reward of up to $1,500.

Copyright 2013 Scripps Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.